1. Field of the Invention
The present invention relates to an intake air heating device of internal combustion engine for motorcycles, adapted to heat the intake air fed to the engine by the heat derived from the exhaust gas to improve the startability of the engine.
2. Description of the Prior Art
In recent years, various types of such internal combustion engines have been proposed and put into practical use as being capable of operating with lean air-fuel mixture to cope with demands for cleaning of the exhaust emissions and reduction in fuel consumption. In the use of these engines, difficulty is often encountered inevitably concerning the starting up of the engine, particularly in the cold start-up of the engine in the districts where the air temperature is comparatively low. As a measure for overcoming the difficulty, it has been proposed to preheat the intake air to be fed to the engine by the heat derived from the exhaust gas to promote the atomization of the fuel in the intake mixture to improve the ignitability of the same.
This countermeasure, however, can hardly be taken in the case of the motorcycles because the intake air heating device cannot find the installation place. Namely, in the case of the internal combustion engines for motorcycles in which the engine and the associated parts are exposed to the open air and mounted in a limited space, it is essential that the intake air heating device can be mounted in a compact manner in a limited space without restricting the mounting conditions of other parts and/or making these parts difficult to access for maintenance. It is also necessary that the comparatively weak portion of the intake air heating device is suitably protected by a member having a high strength.